Im still confused about where i should cut for things like legs? This is where you have big gaps between them that the silcone is gone into, say you have five, im just not sure where to cut? As i thought the idea was to have as small as cut as possible to minimise mould lines???

I've been really trying to wrap my mind around this casting technique by just visualizing the instructions. Probably the most confusing part to me is how to do the whole sprues, like the backpacks shown on the first page.

I was under the impression that you did your cutting on the side or underside of the mold. I get that the sprue is the 'top' of the mold that collects the extra resin and allows for bubbling under vacuum. But does one simply just take that sprue and pull everything out? I'm confused at how you get the entire thing out without damaging the mold, as I would think that those backpacks would not pull free without somehow spraying mold release down in the cracks.

That brings up a second question, as I would think that it would be very difficult to get mold release up in a split mold?

Okay with the mold release, you spray the actual miniature before you pour the silicone to help get the master out of the split mold.

With split molds, you attach the reservoir and sprue piece to the item. Attach it with a small dab of glue so when you bend the mold side to side the connection breaks and you can pull the sprue reservoir out. Then you use a razor to cut open the mold.

This is a cast piece i have. you can see the reservoir and if i move them around especially in the mold the ship hull will come apart from the overflow. (in case you can't read my writing from top to bottom, reservoir, sprue, item)

The mold walls are the box around the item to be cast, you want to make sure the item is fixed in place somehow the silicone can push it around.

A side on look the plastic in the back is supposed to be a wall you want it to go over the end of the item atleast a quarter inch probably more but i'm no pro the ones that know can correct my errors.

Then the tricky part is to cut open the mold using the hook xacto head, i hear this is standard. I myself thought oh i can do a straight exacto and i ended up damaging the detail on the inside of my molds. I've only made 3 split molds and they where all at the same time of super small items with overlapping details. I hated it, I will be doing a split mold for bigger items though the small parts turned me off.

Blindhorizon wrote:Okay with the mold release, you spray the actual miniature before you pour the silicone to help get the master out of the split mold.

Mould release is not necessary on the master part (unless it was made of silicone itself). I've never applied it to any of my masters - the silicone simply doesn't stick to anything.

Blindhorizon wrote:With split molds, you attach the reservoir and sprue piece to the item. Attach it with a small dab of glue so when you bend the mold side to side the connection breaks and you can pull the sprue reservoir out. Then you use a razor to cut open the mold.

Just to clarify some terminology: the sprue and reservoir are pretty much the same thing. The term sprue can be used to refer to most of the non-model parts, but I prefer to delineate the small pieces that connect between the reservoir and part by referring to them as "gates".

Blindhorizon wrote:Then the tricky part is to cut open the mold using the hook xacto head, i hear this is standard. I myself thought oh i can do a straight exacto and i ended up damaging the detail on the inside of my molds. I've only made 3 split molds and they where all at the same time of super small items with overlapping details. I hated it, I will be doing a split mold for bigger items though the small parts turned me off.

I wouldn't call the hooked knife blade standard - I'm personally yet to try it out and get results that are great using just a standard #11 blade. You just gotta be careful when you're cutting up near the master part but thus far I've not done any damage (after literally hundreds of moulds).

It is indeed to fit items of a similar size in one mould and if a model is composed of some really large and really small parts then you're better off keeping them in separate moulds. I do lots of crazily small parts like space ship turrets with no problem in the split moulds so I'm not sure why you had issues Blind. Want to share a pic?

lastspartacus wrote:That brings up a second question, as I would think that it would be very difficult to get mold release up in a split mold?

Not at all. You'll be surprised how flexible the silicone is! You use one hand to spread the mould open and the other to spray the release. Open the mould 90° and apply release to each side from a perpendicular direction.